The purpose of the proposed research program is to define aspects of the molecular structure and regulatory function of defined regions of the Drosophila genome. Initial studies will be directed toward the isolation of the Y chromosome and constructed chromosome fragments; subsequent characterization of the DNA sequences present will be accomplished by DNA/RNA hybridization techniques. Biochemical analysis of the structural organization of the nucleoprotein complex in the Y chromosome, chromosome fragments and heterochromatic regions of the interphase nucleus in pre- and post-blastoderm Drosophila embryos will describe molecular mechanisms of gene inactivation.